The present invention relates to an electrophotographic printer by which information in the form of electrical signals is recorded permanently on a recording medium such as paper.
Electrical signals can be converted to light of varying intensities and an image pattern according to these different light intensities can be recorded on a recording medium such as paper. This principle is employed in the electrophotographic printer the use of which is increasing today.
In the electrophotographic printer, the surface of a photoreceptor coated on a rotating drum accepts and holds a uniform electrostatic charge and, after the uniformly charged surface is illuminated by light from an optical head, the charged image is developed by attracting toner particles. The amount of toner attraction varies with the intensity of light from the optical head and an image pattern according to the difference in the toner density is formed on the surface of the photoreceptor. Electrophotographic printing is completed by transferring this image pattern onto a recording medium such as paper.
The optical heads so far developed for use with electrophotographic printers include a laser scanner, an array of light-emitting diodes, and the combination of a light source and a liquid-crystal shutter cell.
For more details of the electrophotographic printer, see a review entitled "Rapid Expansion of the Market of Desktop Electrophotographic Printers Capable of Document and Simple Video Printouts" in Nikkei Electronics, No. 366, Apr. 8, 1985.
The optical heads used in the prior art electrophotographic printers have various disadvantages. The laser scanner requires the use of a costly scanning mechanism the key component of which is a rotating polygonal mirror. The optical head using an array of light-emitting diodes has the disadvantage of low production rate of LED array. The optical head using a liquid-crystal shutter cell in combination with a light source is unable to attain high printing speeds and has the additional disadvantage of requiring the temperature control of both the liquid-crystal shutter and a fluorescent lamp used as the light source.